This application is based on application No. 11-50028 filed in Japan, the content of which is hereby incorporated by reference.
(1) Field of the Invention
The present invention relates to a fluorescent lamp, and particularly relates to an improvement in the light distribution and impact-resistance of the fluorescent lamp.
(2) Description of Related Art
In general, when a discharge path of a fluorescent lamp is made serpentine, a long discharge path can be formed in a small space, thereby enabling the fluorescent lamp to be miniaturized and to be manufactured as compact as possible.
As one example of such a fluorescent lamp, a bulb-type fluorescent lamp having the following structure is well known. The fluorescent lamp has multiples of U-shaped bulbs or straight bulbs that are set annularly on the upper surface of a holder. The neighboring U-shaped bulbs or straight bulbs are connected to form an arc tube by bridge connection so that a serpentine discharge path is formed as one path. The fluorescent lamp is so provided with an arc tube having the serpentine discharge path, a holder for holding the arc tube, and a base provided at the end of the holder.
This conventional fluorescent lamp has a disadvantage in that a horizontal light distribution of the lamp is likely to be nonuniform. One example of a technique for improving the horizontal light distribution is disclosed in Japanese Laid-Open Patent Application No. 4-267047. The bulb-type fluorescent lamp disclosed in this Application is composed of multiples of U-shaped bulbs set in parallel and a reflective board having a reflective face and being positioned between pairs of legs of the U-shaped bulbs.
This fluorescent lamp is formed by setting the multiples of U-shaped bulbs in parallel. Thus, if this technique is applied to the above-mentioned fluorescent lamp that has the multiples of U-shaped bulbs set annularly, the light distribution may not be adequately improved. Meanwhile, if nothing is provided between the pairs of legs and a reflective cover is attached to the fluorescent lamp, shadow stripes may appear on the surface of the reflective cover.
For the conventional fluorescent lamp, a spacer made of a silicon resin may be set between the neighboring bulbs. By the provision of the spacers, breakages of the bulbs due to impacts, such as an accidental drop during transportation, can be prevented while impact-resistance is ensured. However, manufacture and installation of the spacers increase the materials cost and number of man-hours. Note that xe2x80x9cimpactsxe2x80x9d referred to in this specification means momentary physical shock, such as accidental drop, and also means continuous physical shock, such as a firm grip with a user""s hand.
Additionally, even if the spacers are to be installed, they are independent of the holder and the arc tube. This means that the fluorescent lamp is susceptible to impact given to the entire arc tube and so cannot ensure an adequate impact-resistance.
It is therefore a first object of the present invention to improve the light distribution of a fluorescent lamp that is composed of a plurality of U-shaped bulbs set annularly.
It is a second object of the present invention to provide a fluorescent lamp that can withstand impacts.
The first object of the present invention can be achieved by a fluorescent lamp made up of: an arc tube formed from a plurality of bulbs that are each formed in an inverted U-shape with two substantially straight stems and a curved top and that are joined together into one connected bulb to include one discharge path, an inner surface of each U-shaped bulb being coated with a fluorescent material; a holder having a mounting surface in which the two stems of each U-shaped bulb are planted at positions that lie on an imaginary circle with a roughly the same distance between neighboring U-shaped bulbs; and a light radiating member set in a space enclosed by the holder and the plurality of U-shaped bulbs, and radiating light through each clearance between the two stems and each clearance between neighboring U-shaped bulbs by at least one of reflecting light from the arc tube and emitting light.
With this construction of the fluorescent lamp of the present invention, the light distribution of a fluorescent lamp having a plurality of U-shaped bulbs set annularly can be improved. Also, shadow stripes can be prevented from appearing on the surface of the reflective cover while the lamp is lit up.
Specifically, the light radiating member can be a reflector whose bottom end is fixed to the holder at a center of the imaginary circle, wherein the reflector has a pillar part and a tapered top end, a height of the pillar part measured from the mounting surface being greater than a height of the clearance between the two stems of each U-shaped bulb and smaller than a height of each U-shaped bulb measured from the mounting surface, and wherein, within at least the height of the clearance between the two stems of each U-shaped bulb, a diameter of the reflector is greater than a width of the clearance between the two stems and greater than a width of the clearance between neighboring U-shaped bulbs.
The second object of the present invention can be achieved by a fluorescent lamp made up of: an arc tube formed from a plurality of bulbs that are joined together into one connected bulb to include one discharge path, each inner surface of the plurality of bulbs being coated with a fluorescent material; a holder having a mounting surface in which each mounting end of the bulbs is planted; a supporting member whose bottom end is fixed to the holder on the mounting surface; and a restrictive member that is supported by the supporting member, wherein a positional relationship between the restrictive member and the supporting member is fixed, and that imposes a restriction on the plurality of bulbs so that each bulb substantially remains in an initial position in both horizontal and vertical directions.
With this construction, each bulb will always remain in its initial position in the horizontal and vertical directions by the provision of the restrictive member. The restrictive member also ensures the impact-resistance, thereby making the lamp less prone to breakages resulting from impacts. The restrictive member is situated according to a fixed positional relationship with the supporting member whose bottom end is fixed to the holder, so that the lamp is made resistant to impacts given to the entire arc tube.
It is more preferable for the restrictive member to have one of the following constructions to prevent breakages. The restrictive member preferably has at least two parts that extend from the supporting member and are respectively positioned in a corresponding number of clearances between neighboring bulbs, and each of the at least two parts has an elasticity to absorb a force that is applied to a front of the part in a direction of a space enclosed by the plurality of bulbs. Alternatively, the restrictive member preferably has at least two parts that extend from the supporting member and are respectively positioned in a corresponding number of clearances between neighboring bulbs, and each of the at least two parts has an elasticity to absorb a force that is applied to sides of the restrictive member in a lateral direction.
The supporting member can be a reflector that reflects light from the arc tube. With this reflector, the impact-resistance of the lamp can be ensured and the light distribution can be improved.